doi 10.1287/inte.1060.0252 ©2006 INFORMS Defending Critical Infrastructure

We apply new bilevel and trilevel optimization models to make critical infrastructure more resilient against terrorist attacks. Each model features an intelligent attacker (terrorists) and a defender (us), information transparency, and sequential actions by attacker and defender. We illustrate with examples of the US Strategic Petroleum Reserve, the US Border Patrol at Yuma, Arizona, and an electrical transmission system. We conclude by reporting insights gained from the modeling experience and many “red-team ” exercises. Each exercise gathers open-source data on a real-world infrastructure system, develops an appropriate bilevel or trilevel model, and uses these to identify vulnerabilities in the system or to plan an optimal defense. Key words: critical infrastructure protection; bilevel program; trilevel program; mixed-integer program; homeland security; homeland defense. History: This paper was refereed. Our national strategy for homeland security deemsthese 13 infrastructure sectors critical to the United States: agriculture, banking and finance, chem-ical industry, defense industrial base, emergency ser-vices, energy, food, government, information and telecommunications, postal and shipping, publi